1. Field of the Invention
This invention pertains generally to heaters utilizing oil as fuel, and more particularly to heaters adapted to the burning of oil of varying viscosities such as waste oil.
2. Description of the Prior Art
In order to provide combustion of the oil consumed by an oil heater, it is necessary to vaporize or atomize the oil to allow a proper oil-air mixture to be formed. Oil furnaces operating on standard grades of heating oil often utilize atomization of the oil, while smaller oil space heaters may provide the required combustible fuel-air mixture by vaporization of the oil by heating it to or near the boiling point of the oil. The oil vaporized by heating rises and draws air therewith to form the desired fuel-air mixture.
In oil space heaters in which the combustion mixture is formed by vaporization of the oil, the rate at which oil is supplied to the vaporization pan may be controlled manually or by thermostatically regulated valves such as a needle valve. Such oil heaters are not well adapted to on-off control of the oil being supplied to the vaporizing pan, since the pan must be maintained at a high enough temperature to vaporize the oil being supplied to it. Thus, if oil is shut off for a substantial period of time, combustion in the combustion chamber will cease and the vaporizing pan will cool down to the point that further vaporization of oil supplied thereto will not occur.
Supplying a controlled flow of oil to a vaporizing type oil heater becomes difficult where the oil heater is intended to operate on varying grades of fuel oil having varying viscosities, such as where the oil being burned is waste oil or discarded oil such as crankcase oil, hydraulic oil, various lubricating oils, and mixtures of various grades of oils. Because of the varying viscosities of such oil, common flow control techniques such as needle valves cannot be utilized to maintain a steady flow. Moreover, sediment and dirt particles are often countered in waste oil, and thus the oil line must contain no small orifices or other obstructions in the path of the oil flow if clogging of the oil line is to be avoided. It is nonetheless desired that the rate at which combustion occurs be controlled so that the oil heater may be turned up to a high temperature at a high constant oil flow rate where the ambient temperature surrounding the heater is below a selected temperature. It is also desired that the oil flow to the vaporizing pan be maintained at a selected very low rate to simply maintain vaporization and combustion within the heater when the temperature surrounding the heater is above a selected temperature. This is accomplished in some oil heater systems by the manual shifting of mechanical gears between the drive motor and the pump which pumps oil to the heater.